1. Field of the Invention
The present invention concerns a device for adjusting and controlling the temperature of a liquid. The invention also concerns a method of fabricating such a device.
2. Description of the Related Art
In the field of chemical processing, it is often desirable to provide a device capable of adjusting and controlling the temperature of a liquid processing bath. Often, it is desirable to be able to maintain the temperature of the liquid contained in such a device within a fairly narrow temperature range. Thus, it is desirable to be able to both heat the liquid and cool the liquid. The task of providing a device capable of adjusting and controlling the temperature of a chemical processing solution is rendered more difficult when the chemical processing solution is highly corrosive in nature.
It is known that containers or tanks suitable for holding corrosive chemical processing baths can be fabricated from metal, glass or polymeric resinous material, and that plastic tanks can be rotationally molded. See "The Engineers' Guide to Designing Rotationally Molded Plastic Parts", Association of Rotational Molders (1982). Glass and polymeric resinous materials are often employed because they are often more resistant to the corrosive effects of the processing bath than, for example, metal. Plastic vessels are preferred to glass or quartz because plastic vessels are less sensitive to damage from impact or thermal shock and also because they provide superior chemical resistance in some applications (HF). The disadvantage of plastic vessels is their low thermal conductivity as compared to glass or metal vessels. Thus, whereas heating and cooling is readily accomplished through the vessel walls of a glass or metal vessel, such heating or cooling is difficult if not impossible through the vessel walls of a plastic vessel.
When it is desirable to adjust and control the temperature of such corrosive chemical processing baths contained within a glass or polymeric resinous holding container, several methods have been employed. In some instances, metal heating coils or cooling coils are directly inserted into the chemical processing bath. Unfortunately, the corrosive chemical baths often have a deleterious effect on the heating or cooling coils thus leading to their eventual failure. Alternatively, it has been proposed to coat the metal heating or cooling coils with a corrosion resistant plastic. Again, this approach has proven unsatisfactory in that the chemical processing bath eventually corrodes metal parts associated with the plastic coated heating or cooling coils due to the constant exposure of the plastic to the corrosive bath. Additionally, the use of such coils, coated or uncoated, is undesirable in those instances where it is necessary to be able to both heat and cool the chemical processing bath since, generally, separate coils are needed for heating and cooling. Therefore, two sets of coils may need to be included in the tank, thus substantially complicating the device and occupying a substantial portion of the volume of the tank. Moreover, coils additionally create bath cleaning problems which aggravate conditions in high purity applications.
Alternatively, prior methods have employed a heating or cooling jacket surrounding the exterior of the holding container or tank. Unfortunately, heating or cooling jackets are undesirable in that the heat exchange surface is restricted to the surface of the container, thus limiting their efficiency. Moreover, the heating or cooling jackets are often fabricated from metal parts which are corroded by spills of the chemical processing bath or corroded by fumes from the processing baths.
For the above reasons, known methods of adjusting and controlling the temperature of polymer corrosive chemical processing baths have proven unsatisfactory.